An individual's leptin level is determined by a leptin serum test, according to the University of Rochester Medical Center. The test measures how much leptin is in the bloodstream. During the procedure, a technician uses a needle to draw a blood sample from a vein in the patient's arm.
Leptin is a regulatory hormone that helps control appetite and energy level, explains the University of Rochester Medical Center. A physician orders the test done to determine how much body fat a patient has. The test is also useful for diagnosing the cause of delayed puberty. Women typically have higher levels of leptin. In addition, the hormone level tends to go down as people become older.
Leptin is produced by the body's fat cells, Mayo Clinic states. The hormone circulates through the blood to the brain. When the leptin level reaches a certain amount, the brain determines that the body has sufficient energy stored in fat cells to perform necessary functions. These include using energy, eating and exercising at normal levels. An individual's leptin level is most likely genetically determined.
When people lose weight, they also lose some of the contents of their fat cells, says Mayo Clinic. This reduces leptin production. If the hormone's level goes below its determined threshold, the brain senses that the body is starving. To re-establish the leptin level, the body reacts by eating more food.